Zick's analysis on steel penstock? 2

[woodeispare]

Hello,

I am working to determine the minimum thickness of a set existing steel penstocks (14' diameter steel pipes). The penstocks are supported every 15' by concrete saddles and there is some noticeable buckling around the horns of the saddles. I have seen the stress at this point called Zick's stress in some papers on penstocks. Would it be possible to use this method to do determine the stress from the support, and if so where could I find the formulas and methods used.

Thank you.

 

[MJCronin]

Way, way back in the past.... before you were born, the US Department of the interior got it right....

In 1949, they published an analytic guideline on "Welded Steel Penstocks" giving design methodologies to the masses.

http://www.usbr.gov/pmts/hydraulics_lab/pubs/EM/EM03.pdf

Full-circle stiffener rings at support points are strongly suggested.

Hope that this helps.....

Please tell us more details about your stress analysis and the results of your study.

Where is the penstock located ?

(BTW... I was born in 1949..)

MJCronin
Sr. Process Engineer

 

[woodeispare]

Thanks for the information.

The penstocks are actually even older...they are made from riveted steel and were built around 1910-15. I have been able to calculate the hoop, shear, and bending stress. I know that the hoop stress from internal pressure is the most significant, however I want to also loo into stress at the supports since they are already starting to show deformation.

 

[MarGwy]

Another good reference book is ASCE Manuals and Reports on Engineering Practice No. 79 (ASCE MOP 79), Second Edition, 2012.

 

[woodeispare]

Thanks for the replies. I put in a request for the ASCE Steel Penstocks Manual, hopefully it will be in soon.

Another issue I haven't been able to nail down is the water hammer caused by closing the gates. The way the headworks are set up there are five separate gates that control flow through each penstock.

 

[MJCronin]

If you are trying to evaluate riveted penstocks that are about hundred years old..... good luck.

This installation predates the use of controlled plate steel (i.e. A36, A286, A515) so the properties and microstructure of this plate are anyones guess.

Tell the MBA who wants to use this antique for another hundred years that it is time for a new construction with new materials.

Nothing lasts forever.....

MJCronin
Sr. Process Engineer

 

[LittleInch]

MJC well said.

I had to go look up zick stress and quick quickly found this -

http://lms.i-know.com/pluginfile.ph...resses in Large Horizontal Cylindrical PV.pdf

and this explanation

Saddles for horizontal tanks are usually designed based on the work of L.P. Zick "Stresses in Large Horizontal Cylindrical Pressure Vessels on Two Saddle Supports" first published in September 1951 "THE WELDING JOURNAL RESEARCH SUPPLEMENT."

http://www.codeware.com/support/papers/zick.pdf

This has nothing to do with supports for a pipe, IMHO.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way